underdrive pulley
Team Owner
Joined: Mar 2001
Posts: 25,889
Likes: 7
From: Virginia Beach
CI 3-5-6-7-8 Veteran
An underdrive pulley replaces the main serpentine and AC pulley that's on the front of your crank. It's named as such because it underdrives your engine accessories.
The pulley itself is smaller so for every 1 turn of the crank the accessories like you water pump, AC, powersteering etc turn a little slower, thus reducing parasitic loss.
The pulley itself is smaller so for every 1 turn of the crank the accessories like you water pump, AC, powersteering etc turn a little slower, thus reducing parasitic loss.
Drifting
Joined: Jun 2002
Posts: 1,847
Likes: 1
From: Iowa
Cruise-In IV Veteran
Cruise-In V Veteran
An underdrive pulley replaces the main serpentine and AC pulley that's on the front of your crank. It's named as such because it underdrives your engine accessories.
The pulley itself is smaller so for every 1 turn of the crank the accessories like you water pump, AC, powersteering etc turn a little slower, thus reducing parasitic loss.
The pulley itself is smaller so for every 1 turn of the crank the accessories like you water pump, AC, powersteering etc turn a little slower, thus reducing parasitic loss.
Another question being, is that parasitic loss something of real value to a street-driven Vette, or is it's benefits only realized at the upper RPM range? And even then, how much benefit?
I would think, that in a hot climate the idea of a slower rotating pulley, would not be conducive to an efficiently functioning air conditioner in traffic....
....nor a slower than normal water pump doing a very good jub of keeping the water moving through the radiator.
And this doesn't even take into consideration the voltage drop from running the alternator slower than its intended design parameters.
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 447
From: Atlanta metro Ga.
None of the items you listed are of concern in real-world applications.
The A/C still cools, the water pump still circulates, the alternator still creates amperage.
Technically there must be a HP gain from 1 RPM to redline, of course the higher the RPM the greater the benefit.
Estimates are approx. 7 to 10 HP.
If you need to replace the pulley (defective), only makes sense to pick up "free" HP.
The A/C still cools, the water pump still circulates, the alternator still creates amperage.
Technically there must be a HP gain from 1 RPM to redline, of course the higher the RPM the greater the benefit.
Estimates are approx. 7 to 10 HP.
If you need to replace the pulley (defective), only makes sense to pick up "free" HP.
Team Owner
Joined: Mar 2001
Posts: 25,889
Likes: 7
From: Virginia Beach
CI 3-5-6-7-8 Veteran
Underdrive pulleys are a good thing for cars that see a good bit of extended high RPM use i.e. trackdays. Spinning the accessories slower keeps them cooler and functioning better.
I have an ATI super damper going on my car, but it's only 10% underdriven.
I have an ATI super damper going on my car, but it's only 10% underdriven.
Le Mans Master
Joined: Sep 2003
Posts: 6,253
Likes: 222
From: Farmington CT
Cruise-In VII Veteran
.......but, the a/c diameter on the UD pulleys(powerbond in this ex.) remains the same as oem, thus no loss in a/c efficiency
others from ATI and ASP may be different
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Burning Brakes
Joined: Apr 2003
Posts: 908
Likes: 2
From: TROY MI
Another question being, is that parasitic loss something of real value to a street-driven Vette, or is it's benefits only realized at the upper RPM range? And even then, how much benefit?
I would think, that in a hot climate the idea of a slower rotating pulley, would not be conducive to an efficiently functioning air conditioner in traffic....
....nor a slower than normal water pump doing a very good jub of keeping the water moving through the radiator.
And this doesn't even take into consideration the voltage drop from running the alternator slower than its intended design parameters.
I would think, that in a hot climate the idea of a slower rotating pulley, would not be conducive to an efficiently functioning air conditioner in traffic....
....nor a slower than normal water pump doing a very good jub of keeping the water moving through the radiator.
And this doesn't even take into consideration the voltage drop from running the alternator slower than its intended design parameters.
Pro
Joined: Sep 2005
Posts: 593
Likes: 5
From: Murphy TX
There is significant labor involved in installing an underdrive pulley on a C5. IMO this is why people install a cam when they install an underdrive pulley or vice versa, as it isn't too much more labor to do the can install if the pulley is off.
Banned Scam/Spammer
Joined: Jul 2006
Posts: 2,911
Likes: 10
From: Simi Valley CA
The Alt is the only thing that may need an overdrive pulley. No change needed for a 10% underdrive, but 25%-30% underdrive.. you should put an overdrive on Alt. They are rated Volt/Amp at RPM. You'll find that the "around town" driving won't sufficiently charge the battery.
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 447
From: Atlanta metro Ga.
The Alt is the only thing that may need an overdrive pulley. No change needed for a 10% underdrive, but 25%-30% underdrive.. you should put an overdrive on Alt. They are rated Volt/Amp at RPM. You'll find that the "around town" driving won't sufficiently charge the battery.
If you had an A4, then you might possibly experience an issue.
Last edited by Dan_the_C5_Man; Jan 18, 2007 at 02:39 PM.
Drifting
Joined: Dec 2005
Posts: 1,720
Likes: 3
From: East Hampton CT
I've had my 25% underdrive and it works fine for the alternator. I was concerned that it wouldn't charge properly but even at idle the voltage is right up there (14.5 volts) which is an indication of a high amperage charging condition (output voltage needs to be higher than the battery in order to charge it).However, I noticed that my water pump doesn't spin as quickly as it used to at cruise and thus the car "heats up" more after extended cruising at low rpm. However a quick drop down to 5th gear gets the coolant circulating faster and cools the car down quickly. Something to think about if you have high ambient temps for long distances on the highway where you live.
Banned Scam/Spammer
Joined: Jul 2006
Posts: 2,911
Likes: 10
From: Simi Valley CA
My statement came from:
1) My Chevy dealer Service Mgr who is a good friend.
2) The mechanic who installed my harmonic balancer.
3) The bone-heads who sold me the kit (obviously their first priority is selling. (RPM Outlet... NEVER AGAIN)
Since I heard it from all of them, and then experienced it, I thought it to be true.
Now, having said all that... It may not have been an issue if I had swapped the 2.73s out of there BEFORE the balancer. So may just be an A4/2.73 issue and no one clarified it.